Exemplary embodiments of the present invention relate to a method for fabricating a semiconductor device, and more particularly, to a semiconductor device having buried bit lines each connected to a one-side-contact, and a method for fabricating the same.
Conventional planar metal oxide semiconductor field effect transistors (MOSFET) are reaching their physical limitations with respect to leakage current, on-current, short channel effect, and further miniaturization of conventional MOSFETs is becoming more difficult. To overcome such limitations, semiconductor devices with vertical channels instead of typical planar channels are being developed.
A semiconductor device with vertical channels is fabricated by forming an annular gate electrode (hereafter referred to as “a vertical gate”) surrounding an active pillar which is vertically extended over a semiconductor substrate and forming a source region and a drain region in the upper and lower portions of the active pillar with the gate electrode at the center.
FIG. 1 is a cross-sectional view of a conventional semiconductor device having vertical channels. Referring to FIG. 1, a plurality of pillar structures, each including an active pillar 12 which is extended perpendicularly to a substrate 11 and a hard mask layer 13. The external wall of the active pillar 12 is surrounded by a gate insulation layer 14 and a vertical gate 15, and buried bit lines 16 are formed inside the substrate 11 through an ion implantation of impurities. A trench 17 separating adjacent buried bit lines 16 from one another is filled with an interlayer dielectric layer 18. Word lines 19 are formed in a direction crossing the buried bit lines 16 while connecting adjacent vertical gates 15 to each other.
In the conventional semiconductor device, the buried bit lines 16 at the lower portion of the vertical gate 15 are formed by implanting a dopant through an ion implantation process. However, in miniaturizing semiconductor devices, reducing the resistance of a buried bit line 16 only with the dopant implantation becomes difficult and thus desired characteristics of the semiconductor devices are not obtained.